This study will examine the bulk electrical properties of tumor and normal tissues tissues in the frequency range of actual or proposed diagnostic or therapeutic applications of electromagnetic energy. Dielectric measurements will be performed on freshly excised canine tissue samples including a range of normal tissues, and tissues from excised spontaneous tumors in the dog. The tissue samples will be histologically characterized, and the relation between major variables of tissue structure and dielectric properties will be examined. Special emphasis will be placed on (a) the dielectric properties of tissues at frequencies below 10 MHz where pronounced differences exist in the dielectric properties of tumor and adjacent normal tissues, and (b) on adipose tissues, which exhibit a large range of dielectric properties and for which significant hazard exists in some hyperthermia applications from overheating.